1. Field of the Invention
The invention is directed to an improved fuel supply system for internal combustion engines.
2. Description of the Prior Art
One fuel supply system of the type with which this invention is concerned. known for instance from German Patent Disclosure DE 198 20 264 A1. has a housing in which a pistonlike element is disposed longitudinally displaceably in a bore. The pistonlike element, which can be embodied as a valve needle, for instance, is guided sealingly in the bore in a guide portion of the bore. On one end of the guide portion, a first fuel-filled chamber adjoins the guide portion, and on the other end of the guide portion, a second fuel-filled chamber adjoins it. Because of the sealing guidance, only severely throttled fuel can flow from one fuel-filled chamber into the other through the annular gap formed between the pistonlike element and the wall of the bore, and in the annular gap the fuel forms a lubricating film.
In the fuel supply system, which can for instance be a fuel injection valve for internal combustion engines, the pistonlike element moves in the bore in the longitudinal direction. The result can be wear between the pistonlike element and the wall of the bore. To minimize wear, especially whenever a pressure difference prevails between the first fuel-filled chamber and the second fuel-filled chamber, various provisions are known, such as various kinds of structuring and coatings of the pistonlike element. In DE 198 20 264 A1, flutelike grooves on the guide portion of the pistonlike element are shown, which are embodied there at various depths and with various widths and in various arrangements. However, this does not take into account the fact that the first and second fuel-filled chambers of the fuel supply system are not the same in their function and in terms of the pressures that occur there, and that the pistonlike element for instance moves at different speeds in the two longitudinal directions. As a result, the lubricating film between the guide portion of the pistonlike element and the wall of the bore is not always embodied optimally.